Crystal Defects Research Articles

Rapid Room Temperature Entropy‐Stabilized Synthesis Enabling Super‐Stable Metal Halide Perovskite Semiconductor Colloidal Nanocrystals

AbstractAlthough high‐entropy materials have garnered extensive attention due to their substantially enhanced performance, their formation generally demands prolonged high‐temperature synthetic processes. Moreover, research on entropy‐stabilized halide perovskite (ESHP) semiconductor colloidal nanocrystals (NCs) is scarce. Herein, a highly efficient and rapid room temperature (RT) entropy‐stabilized approach in air is proposed, involving the concurrent incorporation of multi‐metal cations for the synthesis of high‐quality all‐inorganic ESHP NCs with near‐unity quantum yield and excellent colloidal stability. Remarkably, even after 8 months of aging in air, the ESHP NCs exhibited superior emission characteristics with a single‐exponential decay and maintained the initial NC monodispersity. Density functional theory calculations further demonstrated that the outstanding performance of ESHP NCs originated from the diminished crystal defects and a more robust octahedral structure. Significantly, this RT entropy‐driven synthesis can be extended to metal halide semiconductor NCs with diverse composition systems. The findings inspire new perspectives for entropy‐stabilized, high‐performance metal halide perovskite NCs toward versatile applications.

Non-Volatile Multifunctional Dipole Molecules Enable 19.2% Efficiency for Printable Mesoscopic Perovskite Solar Cells.

Dipole molecules (DMs) show great potential in defect passivation for printable mesoscopic perovskite solar cells (p-MPSCs), although the crystallization process of p-MPSCs is more intricate and challenging than planar perovskite solar cells. In this work, a series of non-volatile multifunctional DMs are employed as additives to enhance the crystallization of perovskites and improve both the power conversion efficiency (PCE) and stability of the devices. This enhancement is achieved by regulating the side groups of benzoic acid molecules with the electron-donating groups such as guanidine (─NH─C(═NH)─NH2), amino (─NH2) and formamidine (─C(═NH)─NH2). DMs form hydrogen bond interactions with the organic cations of perovskite and establish electrostatic interactions with PbI6 4-. The synergistic effect of these interactions suppresses PbI2 formation, enhances perovskite film crystalline quality, reduces perovskite crystal defect density, mitigates non-radiative recombination, and effectively enhances carrier transfer and extraction efficiency. Furthermore, the incorporation of DMs leads to a reconstruction of the perovskite film surface energy level, thereby enhancing hole extraction efficiency at the perovskite/carbon electrode interface. The optimized p-MPSCs achieve a PCE of 19.23%. The unencapsulated device demonstrates promising long-term storage stability, retaining 91% of the original PCE after 1440 h of aging at 40 ±5% relative humidity and 30 ±5°C.

Computational microscopy with coherent diffractive imaging and ptychography.

Microscopy and crystallography are two essential experimental methodologies for advancing modern science. They complement one another, with microscopy typically relying on lenses to image thelocal structuresof samples, and crystallography using diffraction to determine the global atomic structure of crystals. Over the past two decades, computational microscopy, encompassing coherent diffractive imaging (CDI) and ptychography, has advanced rapidly, unifying microscopy and crystallography to overcome their limitations. Here, I review the innovative developments in CDI and ptychography, which achieve exceptional imaging capabilities across nine orders of magnitude in length scales, from resolving atomic structures in materials at sub-ångstrom resolution to quantitative phase imaging of centimetre-sized tissues, using the same principle and similar computational algorithms. These methods have been applied to determine the 3D atomic structures of crystal defects and amorphous materials, visualize oxygen vacancies in high-temperature superconductors and capture ultrafast dynamics. They have also been used for nanoscale imaging of magnetic, quantum and energy materials, nanomaterials, integrated circuits and biological specimens. By harnessing fourth-generation synchrotron radiation, X-ray-free electron lasers, high-harmonic generation, electron microscopes, optical microscopes, cutting-edge detectors and deep learning, CDI and ptychography are poised to make even greater contributions to multidisciplinary sciences in the years to come.

Atomic Imprint Crystallization: Externally-Templated Crystallization of Amorphous Silicon

In this paper, we demonstrate the crystallization of an amorphous Si layer via atomic imprint crystallization (AIC), where an amorphous Si layer is crystallized by solid phase epitaxy (SPE) from an externally impressed single-crystal Si template that is then peeled off via delamination following crystallization. Microstructural analysis using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) studies of the delaminated (crystallized) films reveals that the top surface of the amorphous Si layer is crystallized by SPE with regions (up to ∼5 mm diameter) composed of epitaxial domains (lateral size of few μm), all of which bear the same crystalline orientation as that of the template crystal. Unlike conventional SPE, the crystallization is not uniform across the entire region: the grains contain crystal defects such as dislocations, stacking faults, and twins; and while the crystallization is initiated at the top surface of the film, the thickness of the single-crystalline area is limited to ∼40 nm from the top surface. Clearly, the AIC approach leads to SPE (aligned with the template’s crystalline orientation) over areas as large as few mms, but the crystallization is defective and incomplete through the film. We attribute this to be a consequence of the tensile stress field created at the amorphous/crystalline frontline by the volume change of amorphous Si during the crystallization. Our results establish the feasibility of imprint crystallization, and points to the direction of a new process that may enable the creation of single crystal pockets in integrated device stacks in a scalable fashion without the need for an underlying single crystal substrate. However, our results also indicate that the crystallization is of a poor quality and indicates the need for further optimization of the crystallization method.

Analytical model for the motion and interaction of two-dimensional active nematic defects.

We develop an approximate, analytical model for the velocity of defects in active nematics by combining recent results for the velocity of topological defects in nematic liquid crystals with the flow field generated from individual defects in active nematics. Importantly, our model takes into account the long-range interactions between defects that result from the flows they produce as well as the orientational coupling between defects inherent in nematics. Our work complements previous studies of active nematic defect motion by introducing a linear approximation that allows us to treat defect interactions as two-body interactions and incorporates the hydrodynamic screening length as a tuning parameter. We show that the model can analytically predict bound states between two +1/2 winding number defects, effective attraction between two -1/2 defects, and the scaling of a critical unbinding length between ±1/2 defects with activity. The model also gives predictions for the trajectories of defects, such as the scattering of +1/2 defects by -1/2 defects at a critical impact parameter that depends on activity. In the presence of circular confinement, the model predicts a braiding motion for three +1/2 defects that was recently seen in experiments, as well as stable and ergodic trajectories for four or more defects.

Effect of hot isostatic pressing treatment on the thermoelectric power factors of zinc oxides

The effect of hot isostatic pressing (HIP) on the thermoelectric power factor of zinc oxide (ZnO) has been examined. ZnO is expected to be a potential n-type oxide thermoelectric material that could enhance the thermoelectric conversion efficiency. The HIP treatment is useful for densifying the material and controlling crystal defects in the material by applying high temperatures and pressures simultaneously. Furthermore, the atmosphere during HIP treatment can be controlled to enable the application of this technique to both metallic and oxide materials. The thermoelectric power factor of ZnO increased due to a notable increase in electrical conductivity, although the Seebeck coefficient decreased by approximately 50% following HIP treatment under argon gas. The increase in the thermoelectric power factor is attributed to the oxygen vacancies introduced into ZnO subsequent to the HIP treatment. Consequently, HIP treatment represents a promising approach for enhancing the thermoelectric power factor of ZnO.

Scalable Reshaping of Diamond Particles via Programmable Nanosculpting.

Diamond particles have many interesting properties and possible applications. However, producing diamond particles with well-defined shapes on a large scale is challenging because diamonds are chemically inert and extremely hard. Here, we show that air oxidation, a routine method for purifying diamonds, can be used to precisely shape diamond particles at scale. By exploiting the distinct reactivities of different crystal facets and defects inside the diamond, layer-by-layer outward-to-inward and inward-to-outward oxidation produced diverse diamond shapes including spheres, twisted surfaces, pyramidal islands, inverted pyramids, nanoflowers, and porous polygons. The nanosculpted diamonds had more and finer features that enabled them to outperform the original raw diamonds in various applications. Using experimental observations and Monte Carlo simulations, we built a shape library that guides the design and fabrication of diamond particles with well-defined features that could be critical for anticounterfeiting, optical, and other practical applications. Our study presents a simple, economical, and scalable way to produce shape-customized diamonds for various potential technologies.

Zwitterion additive-assisted crystal growth regulation and defect passivation for high-performance inorganic perovskite solar cells

Inorganic CsPbI2Br perovskites solar cells (PSCs) have attracted extensive interest owing to their outstanding optoelectronic properties. Nevertheless, the undesirable perovskite film quality and severe charge recombination dramatically restrict their performance improvement. Herein, we propose an additive strategy to modulate the CsPbI2Br crystallization process and reduce the defect density by adding 3-(1-pyridinio)-1-propanesulfonate (PPS) zwitterionic molecules into the perovskite precursor solution. The incorporation of PPS zwitterion can not only retard the crystal growth rate of CsPbI2Br with uniform morphology and enlarged grain size, but also effectively passivate defects via interacting with the uncoordinated sites in the perovskite film. In addition, the PPS zwitterion greatly ameliorates the energy level alignments at the interface. Thus, the photogenerated carriers are more efficiently extracted, and the nonradiative recombination is significantly suppressed. With these benefits, the optimized PPS-based CsPbI2Br device delivers a champion efficiency of 16.37% with high open-circuit voltage (VOC) of 1.302 V in contrast to the pristine device with an inferior efficiency of 14.26% (VOC of 1.183 V). In addition, the unencapsulated device with PPS presents improved long-term stability by preserving ∼85% of the initial efficiency after 760 h storage in ambient atmosphere. These findings provided important insights into the additive strategy of using zwitterionic materials for constructing efficient and stable inorganic PSCs.

Microstructural, morphological, and optical properties of Fe2O3 nanoparticles obtained from Fe-MIM MOF

Abstract This study explores the microstructural, morphological, and optical properties of Fe2O3 nanoparticles synthesized from the pyrolysis of ZIF-8 like Fe-MIM metal-organic frameworks (MOFs). Using X-ray diffraction (XRD) profile analysis methods, including the modified Scherrer, Williamson-Hall (W-H), size strain plot, and Halder-Wagner methods, the impact of annealing temperature on the microstructural parameters and crystal defects of the obtained Fe2O3 nanoparticles was investigated. The nanoparticles exhibited high crystallinity and a rhombohedral α-Fe2O3 phase. Morphological analysis through transmission electron microscopy (TEM) revealed distinct structural features, while UV-vis spectroscopy was employed to examine their optical properties. The results indicated that higher annealing temperatures enhance crystallinity, reduce defect density, and improve atomic mobility. This comprehensive analysis provides valuable insights into the synthesis-structure-property relationships of Fe2O3 nanoparticles, highlighting their potential applications in many applications.

Control of Integrated Circuits Crystals' Surface Microrelief and Defects of Heteroand Submicrostructures by the Atomic Force Microscopy Method

The aim of the work was to study the structure and defects of a channel transistor with two types of conductivity (p and n), the submicrostructures based on nickel silicide films, and the seed layers based on AlN using atomic force microscopy (including conductive or electric force method, which allow one to study the electrical conductivity of the material surface). The influence of the manufacturing technology and local oxide formation on the relief and structure of the pand n-type transistor was established. The local oxide is necessary for the electrical isolation of the transistors from each other. The surface roughness is higher on the surface and outside the p-channel transistor than on the n-channel transistor. When examining the AlN layers both in the topography mode and in the adhesion mode, defects in the form of pores were revealed, which are places of electrical breakdowns, which worsens the properties of the such heterostructures. With an increase in the temperature and time of nitriding, the defects of the AlN layers significantly decrease. The conductive areas on the surface of the nickel silicides after rapid thermal treatment at 300 and 400 °C using electric force microscopy were detected, which shows incomplete formation of nickel silicide during the treatment. Thus, the efficiency of the atomic force microscopy method using a specialized conductive technique as a method for monitoring microelectronic components was demonstrated.

Hybrid Strategies for Enhancing the Multifunctionality of Smart Dynamic Molecular Crystal Materials.

Dynamic molecular crystals are an emerging class of smart engineering materials that possess unique ability to convert external energy into mechanical motion. Moreover, they have being considered as strong candidates for dynamic elements in applications such as flexible electronic devices, artificial muscles, sensors, and soft robots. However, the inherent defects of molecular crystals like brittleness, short-life and fatigue, have significantly impeded their practical applications. Inspired by the concept of "the whole is greater than the sum of its parts" in the field of biology, building stimuli-response composites materials can be regarded as one of the ways to break through the current limitations of dynamic molecular crystals. Moreover, the hybrid materials can exhibit new functionalities that cannot be achieved by a single object. In this review, the focus was placed on the analysis and discussion of various hybrid strategies and options, as well as the functionalities of hybrid dynamic molecular crystal materials and the important practical applications of composite materials, with the introduction of photomechanical molecular crystals and flexible molecular crystals as a starting point. Moreover, the efficiency, limitations, and advantages of different hybrid methods were compared and discussed. Furthermore, the promising perspectives of smart dynamic molecular crystal materials were also discussed and the potential directions for future work were suggested.

Controlling the Mechanism of Nucleation and Growth Enables Synthesis of UiO-66 Metal-Organic Framework with Desired Macroscopic Properties.

By combining in situ X-ray diffraction, Zr K-edge X-ray absorption spectroscopy and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, we show that the properties of the final MOF are influenced by H2O and HCl via affecting the nucleation and crystal growth at the molecular level. The nucleation implies hydrolysis of monomeric zirconium chloride complexes into zirconium-oxo species, and this process is promoted by H2O and inhibited by HCl, allowing to control crystal size by adjusting H2O/Zr and HCl/Zr ratios. The rate-determining step of crystal growth is represented by the condensation of monomeric and oligomeric zirconium-oxo species into clusters, or nodes, with the structure identical to that in secondary building units (SBU) of UiO-66 framework. The rapid crystallization in the absence of HCl leads to formation of defective secondary building units with missing zirconium atoms, providing a pathway to control the number of defects in UiO-66 crystals. Remarkably, we have shown that assembling of the metal nodes and linkers into the UiO-66 structure is not the rate-limiting step, and the degree of deprotonation of the linker has no direct effect on the crystallization kinetics or crystal size of product.

Improvement of recessed MOS gate characteristics in normally-off AlN/GaN MOS-HFETs with N2/NH3 thermal treatment

This study investigated the metal–oxide–semiconductor gate characteristics of recessed-gate AlN/GaN metal–oxide–semiconductor-heterojunction-field-effect transistor with N2/NH3 thermal treatment. The gate-channel mobility in recessed-gate structures formed by the inductively coupled plasma-reactive ion etching method is degraded due to plasma-induced damage. The application of thermal treatment to etch-damaged GaN surfaces was observed to re-form a clear step-terrace structure, effectively reversing the effects of the etching damage. A corresponding enhancement in peak field-effect mobility was experimentally verified, with an increase from a pretreatment value of 656 to 1042 cm2/V·s after thermal treatment. Concurrently, an improvement of the lower gate-leakage current by 1–2 orders of magnitude was measured. This thermal treatment method can reduce crystal defects at deep levels of 1.8–2.9 eV below Ec on the etched GaN surface. In particular, this N2/NH3 thermal treatment approach could potentially contribute to the reduction of deep levels such as atomic displacement, gallium vacancies, and those complexes generated by inductively coupled plasma-reactive ion etching.

Defect-Mediated Energy Transfer Mechanism by Modulating Lattice Occupancy of Alkali Ions for the Optimization of Upconversion Luminescence.

The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na-Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na0.9Li0.1LuF4-Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future.

Construction of low-vacancy hexagonal Prussian blue analogues for efficient rubidium recovery

Prussian blue analogues (PBAs) are considered a promising adsorbent for rubidium recovery due to their high ion exchange capacity and selectivity. However, the development of PBAs-based rubidium adsorbents with excellent stability and adsorption capacity is still hindered by the inevitable CN ligand vacancies. Herein, a synthetic strategy is proposed to slow down crystal nucleation and promote the self-repair of crystal defects by incorporating N-doped porous carbon (NPC) as a solid modifier during the synthesis process. As a result, the vacancy content of Zn-PBA-NPC is significantly decreased and large size twinned crystals are produced, which remarkably improves the thermal and acid-base stability. Benefiting from the high content of K+ in the low-vacancy Zn-PBA-NPC, it achieves a high adsorption amount of 199.1 mg g−1 and rapid adsorption kinetics of just 5 min for Rb+. In addition, it shows good selectivity in the presence of other alkali metal ions. This work not only prepares a high-performance adsorbent for efficient recovery of Rb+, but also facilitates insights into the design and construction of low-vacancy PBAs.

Defect detection and size classification in CdTe samples in 3D

Defects in semiconductor crystals can have significant detrimental effects on their performance as radiation detectors. Defects cause charge trapping and recombination, leading to lower signal amplitudes and poor energy resolution. We have designed and built a modular 3D scanner for analyzing these defects in semiconductor samples using commercial off-the-shelf components. Previous solutions offer great spatial resolution, but have limited sample holding capacity and use continuum light sources which can cause difficulty differentiating between different materials within samples. Our design also includes a modular sample holder allowing for easy changing of samples. In this paper, we showcase first results achieved with this custom built scanner as well as planned developments.

Portable Nuclear Magnetic Resonance Spectrometer with Birdcage Coil for Non-destructive Testing and Analysis of Metallic Materials

Non-destructive testing (NDT) using nuclear magnetic resonance (NMR) spectroscopy for metallic materials is a cutting-edge technique that offers valuable insights into the structure, composition, and properties of metals without altering or damaging the material. NMR spectroscopy is a powerful analytical tool that uses the magnetic properties of atomic nuclei to provide detailed information about the molecular environment of samples. By subjecting metallic materials to NMR analysis, researchers and engineers can gain a deeper understanding of various aspects, such as the crystal structure, defects, impurities, and mechanical properties of metals. The NMR technique can detect the magnetic behavior of metal samples and provide a non-invasive tool for evaluating the quality, integrity and performance of materials. In summary, NMR-based non-destructive testing for evaluating metallic materials provides accurate, quantitative and reliable data that can support decision-making processes, optimize manufacturing methods and ensure the safety and reliability of metallic components. The ability of NMR to probe the atomic-level structure and dynamics of metals makes it an indispensable tool for research and industrial applications in fields ranging from metallurgy and engineering to aerospace and automotive industries. In this article, a portable NMR spectrometer has been designed, simulated and implemented from a small birdcage coil for the frequency range of 1 MHz to 10 MHz according to the static magnetic field. Finally, a portable NMR device for performing NDT of metallic materials is presented, which is created by using a suitable coil, a magnetic field of 230 µT and 95% homogeneity.

High quality perovskite thin films synthesized by low-temperature supercritical carbon dioxide annealing method

Thermal annealing is a conventional method used to eliminate residual solvents in perovskite films, reducing internal and interfacial defects. However, due to the high saturation vapor pressure of the residual solvent dimethyl sulfoxide, it is difficult to quickly remove the residual solvent at low temperatures. In this paper, the high permeability and diffusion of supercritical CO2 (ScCO2) were used to quickly remove the residual solvent of film at low temperatures. The effects of ScCO2 annealing on the surface morphology, residual solvents, internal and interfacial defects of perovskite thin films were investigated. The experimental results indicate that ScCO2 annealing significantly improves the removal efficiency of residual solvents compared to low-temperature annealing, effectively minimizing internal and interfacial defects. Additionally, the interaction energy of CO2 with the perovskite crystal plane reduces the surface energy of the crystal, resulting in a significant increase in the average grain size of the crystal by about 91.2%. Notably, the average crystal size of the film prepared by chlorobenzene as an antisolvent increased from 209.35 nm to 704.57 nm. The high penetration of ScCO2 also promoted uniform crystal growth, thereby reducing crystal structure deformation and defects. The carrier lifetime of perovskite thin films after ScCO2 annealing increased by over 58.8% on average.

Influence of cavity crystal defects on the thermal ecomposition mechanism of NTO

Abstract The impact of cavity crystal defects on the thermal decomposition process of 3-nitro-1,2,4-triazol-5-one (NTO) was examined utilizing the reaction molecular dynamics method. A perfect crystal model of NTO and crystal models with cavity defects at concentrations of 0.78%, 1.17%, 2.34%, 3.13%, and 5.10% were constructed, and the potential energy and product changes in the isothermal mode at 2500 K were calculated. The impact of cavity defects was analyzed for the initial reaction stages, and the thermal decomposition reaction rate of 2500 K was calculated. The results demonstrate that at 2500 K, the complex reaction of NTO is enhanced, with the denitration reaction emerging as the dominant initial reaction type, followed by the ring-breaking reaction, and the proton transfer reaction occurring with a lower frequency. The principal intermediate products were CO2, NO2, HON, etc. The final products included N2, N4, H2O, HO2, and O2. In the range of 0.78% to 2.34% cavity content, the initial chemical reaction rate of NTO exhibited a slowing down trend with the increase of hole concentration. A collapse in the crystal structure accompanied this. Conversely, an acceleration was observed in the initial chemical reaction rate of NTO when the cavity concentration exceeded 2.34%.

Efficient photo-assisted reduction of Cr(VI) via activated carbon mediated Z-scheme FeS2/α-FeOOH/C heterojunction: Focusing on molecular oxygen fate and synergetic reduction mechanism

Herein, pyrite (FeS2), goethite (α-FeOOH) and activated carbon (C) were combined to construct FeS2/α-FeOOH/C composites with C mediated Z-scheme heterojunction for efficient photo-assisted Cr(VI) reduction. Characterization tests indicated the strong interaction via Fe-O-C and C-S-C, the increased amount of crystal defects and surface oxygenic functional groups, and the decreased agglomeration degree during combination strengthened electron transport and visible light conversion efficiency, resulting in synergistic effect for enhanced Cr(VI) removal. Additionally, C mediated Z-scheme heterojunction with lower resistance facilitated the transfer and separation efficiency of photo-generated carriers, further accelerating Cr(VI) reduction. Consequently, almost 100 % of Cr(VI) was reduced via FeS2/α-FeOOH/C in 60 min, 4 times that of pristine FeS2. Quenching, EPR and control experiments confirmed photocatalysis made more contribution than single reductive reagents (FeS2) in Cr(VI) reduction. The specific contribution rate of reductive species like e−, Fe2+, S22− and •O2− in this complicated system was firstly detailedly demonstrated and •O2− played a predominant role under oxic condition. Meanwhile, oxidative species like H2O2, 1O2 and •OH ascribed to DO activation or photo-generated h+ preferred to reacted with Fe2+ and S22− with higher reducibility and-only delayed Cr(VI) reduction rate. Hence, the final total Cr(VI) removal efficiency and generated Cr(III) kept stable in oxic solution.